1. Field of the Invention
The present invention relates generally to improvements in automotive equipment and, more particularly but not by way of limitation, to improvements in brake systems of automotive vehicles.
2. Brief Description of the Prior Art
As is well known, it is not desirable in braking a vehicle for the wheels to lock so that tires slide on the roadway while the vehicle is brought to rest; rather, a vehicle can be stopped in the shortest distance if rolling contact between the tires and the roadway is maintained during braking of the vehicle. Thus, experienced drivers often "pump", or repetitively release, the brakes of their vehicles during braking to ensure that the brakes do not lock up and thereby increase the distance required to bring their vehicles to a stop.
However, while it is well known that brakes should not be continuously operated during the braking of a vehicle, such operation nevertheless frequently occurs as the result of either inexperience on the part of a driver or as a natural reaction to an emergency situation. Since it will often be the case that an emergency will require the halting of a vehicle as quickly as possible, a driver may very well react to the emergency by applying, and maintaining, maximum force on the brake pedal of his vehicle and such reaction may very well exacerbate the emergency by causing sliding of the vehicle to occur. Thus, instead of avoiding the consequences of the emergency situation, he inadvertently causes the consequences to occur, often to the injury of himself or others.
To avoid this danger, anti-lock brake systems have been developed and are offered, often as an option, to purchases of new vehicles. However, prior art anti-lock brake systems; more particularly, the use of such systems, has not provided a complete solution to the problem that brake locking during stops presents. Thus, for example, in prior art anti-locking brake systems, the anti-lock features are often achieved through the use of complex computerized or other electronic circuitry operated from wheel rotation sensors and, consequently, such systems can add a not inconsiderable increase to the purchase price of a vehicle. In large part, the cost of such anti-lock brakes systems stems from the control of the system using sensors that detect the imminence of slipping of individual wheels and operate to prevent slipping on a wheel-by-wheel basis. In the type of driving done by many drivers, this cost cannot be justified with the result that many purchasers of a vehicle will forego the option of anti-lock brakes to avoid the price that must be paid to obtain the option.
Equally important, many older vehicles having brake systems without anti-locking features are on the road and, prior to the present invention, no practical means has been available to provide the brake systems of these vehicles with anti-lock capabilities. A variety of types of brake systems are in current use; for example, vacuum assisted hydraulic, pneumatic and electric so that an anti-lock device that might be suitable for one type of brake system will not be suited to another type. Moreover, components used in brake systems currently in use are not standardized but vary from one vehicle to another. Such variation stems, in part, from engineering choices made by the manufacturers of vehicles and, in part, from variations in types of vehicles that are found on the road. Thus, for example, an anti-lock device that might be suitable for a passenger automobile may not be suitable for a tractor-trailer combination that has the same general type of brake system. Similarly, an anti-lock system that might be suitable for a vehicle having one source of manufacture may not be suited to a vehicle having another source of manufacture. Thus, retrofit of an existing brake system can require, substantially, the replacement of the existing brake system with a brake system having anti-lock features. The cost of such replacement is not acceptable to many vehicle users.
Moreover, tractor-trailer combinations present special problems. As is known in the art, the brakes of a trailer must be applied concurrently with the brakes of the tractor to prevent "jackknifing" of the combination and it is common practice to provide trailers with brake systems that are actuated when deceleration of the tractor occurs. Similarly, the brake system of a trailer may be fully integrated with the brake system of the tractor. However, as is also known, a tractor may be used with different trailers at different times and the brake systems of the trailers may differ from one use to another. Thus, for example, a tractor having a pneumatic brake system may be used with a trailer having a pneumatic brake system on one occasion and with a trailer having an electric brake system on another occasion. Thus, it is often not practical to integrate the trailer brake system with the tractor brake system with the result that the cost of providing both the tractor and the trailer with anti-lock brake systems can be substantial.
Thus, while it is possible, in principle, to adapt prior art anti-lock brake systems to substantially any vehicle operated under substantially any set of circumstances, the cost of doing so militates against the adaption.